Wireless subscriber communication unit and method of power control with back-off therefore

ABSTRACT

A wireless subscriber communication unit comprises a transmitter having a power amplifier and a feedback power control loop having a power control function arranged to set an output power level of the power amplifier. The power control function is arranged to perform a back-off of the output power prior to completion of a transmission burst.

FIELD OF THE INVENTION

This invention relates to power control in a wireless subscribercommunication unit. The invention is applicable to, but not limited to,improving the performance of wireless power amplifier control during aramp-down operation.

BACKGROUND OF THE INVENTION

Wireless communication systems, for example cellular telephony orprivate mobile radio communication systems, typically provide for radiotelecommunication links to be arranged between a plurality of basetransceiver stations (BTS) and a plurality of subscriber units. Anestablished harmonised cellular radio communication system, providingpredominantly speech and short-data communication, is the Global Systemfor Mobile Communications (GSM). GSM is often referred to as 2^(nd)generation cellular technology.

An enhancement to this cellular technology, termed the General PacketRadio System (GPRS), has been developed. GPRS provides packet switchedtechnology on GSM's switched-circuit cellular platform. A yet furtherenhancement to GSM that has been developed to improve system capacitycan be found in the recently standardised Enhanced Data Rate for GlobalEvolution (EDGE) that encompasses Enhanced GPRS (EGPRS). A still yetfurther harmonised wireless communication system currently being definedis the universal mobile telecommunication system (UMTS). UMTS isintended to provide a harmonised standard under which cellular radiocommunication networks and systems will provide enhanced levels ofinterfacing and compatibility with many other types of communicationsystems and networks, including fixed communication systems such as theInternet. Due to this increased complexity, as well as the features andservices that it supports, UMTS is often referred to as a thirdgeneration (3G) cellular communication technology. In UMTS subscriberunits are often referred to as user equipment (UE).

In such cellular wireless communication systems, each BTS has associatedwith it a particular geographical coverage area (or cell). The coveragearea is defined by a particular range over which the BTS can maintainacceptable communications with subscriber units operating within itsserving cell. Often these cells combine to produce an extensive coveragearea.

Wireless communication systems are distinguished over fixedcommunication systems, such as the public switched telephone network(PSTN), principally in that mobile stations/subscriber equipment movebetween coverage areas served by different BTS (and/or different serviceproviders). In doing so the mobile stations/subscriber equipmentencounter varying radio propagation environments. In particular, in amobile communication context, a received signal level can vary rapidlydue to multipath and fading effects.

One feature associated with most present day wireless communicationsystems allows the transceivers in either or both the base stationand/or subscriber unit to adjust their transmission output power to takeinto account the geographical distance between them. The closer thesubscriber unit is to the BTS's transceiver, the less power thesubscriber unit and the BTS's transceiver are required to transmit, forthe transmitted signal to be adequately received and decoded by theother unit. Thus, the transmit power is typically controlled, i.e. setto a level that enables the received signal to be adequately decoded,yet reduced to minimize potential radio frequency (RF) interference.This ‘power control’ feature saves battery power in the subscriber unit.Initial power settings for the subscriber unit, along with other controlinformation, are set by the information provided on a beacon (control)physical channel for a particular cell.

Furthermore, in a number of wireless communication systems, the effectof fast fading in the communication channel is a known and generallyundesirable phenomenon caused by the signal arriving at a receiver via anumber of different paths. Therefore, fast power control loops are oftenadopted to rapidly determine and optimize the respective transmit powerlevel. Such power control loops introduce potential instability problemsinto the transmitter design.

The inventors of the present invention have identified that in the fieldof power control techniques, and particularly at the higher poweramplifier output power levels, for example >30 dBm, the closed loopsystem sometimes does not operate over sufficient bandwidth to track thereference signal rapidly enough, which is as a direct result of thecontrol slope of the PA collapsing.

In the context of the present invention, the expression ‘bandwidth’,with respect to closed loop power control operation of the transmitter,encompasses a speed at which a system responds to an input perturbation.

Once the power amplifier has reacted, the reference signal has alreadyramped down significantly. In this case, the power amplifier outputpower must then drop very dramatically to compensate for the fact thatthe reference signal has already dropped. Invariably, in such asituation, a switching transient hit is incurred, which causes spectraldegradation of the transmit signal.

As a result of these effects, critical standards' specifications arefailed, such as:

-   -   (i) Power versus time (PvT) mask, or    -   (ii) Out-of-band spectral emission performance.

For power amplifiers operating in a closed loop environment, a poorcontrol slope (between the bias input and the detector output)significantly shortens the bandwidth of the system. This is particularlythe case at higher output power levels and provides a sluggishperformance of the power control operation. Typically, it is intendedthat the radio frequency (RF) power output signal tracks a raised cosineprofile response on a ‘ramp-down’ operation.

However, due to the aforementioned sluggish behaviour (hereinafterreferred to as a ‘dead-zone’, as illustrated in FIG. 1), of the poweramplifier, particularly when operating in a ‘closed-loop’ architecture,it takes a finite time (in the order of μsec) for the output to react tothe ramp-down operation. This degrades the transient behaviour at theoutput of the power amplifier, which, in turn, degrades the switchingtransient performance of the transmitter. As a result, unfavourableinterference at adjacent channels occurs that fail to meet, say, the3GPP/ETSI 05.05 specifications.

U.S. Pat. No. 6,625,227 B1, titled “Artificial ramping of transmit powerfor burst transmissions” describes a mechanism for looking at thesymbols used in a transmission and then initiates both ramp-up andramp-down operations based on these symbols. In particular, themechanism proposes modifying ramp profiles to specifically improve phasetransitions.

U.S. Pat. No. 6,553,212 B1, titled “Method and apparatus for improvingloop stability and speed of a power control loop”, describes a mechanismfor assessing a system power and determines how fast/slow the system isat that given power. The document then proposes modifying the gainwithin the feedback path, which effectively modifies the closed loopbandwidth.

A need therefore exists, in general, for an improved power controlarrangement and method of operation, particularly in the case of a poweramplifier performance operating in a closed-loop architecture atrelatively high power output levels.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a wirelesscommunication unit comprising a power control system, a method forcontrolling an output power level of a subscriber communication unit andan integrated circuit therefore, as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will now be described,with reference to the accompanying drawings, in which:

FIG. 1 illustrates a functional block diagram of a wireless subscriberunit, adapted in accordance with one embodiment of the presentinvention;

FIG. 2 illustrates a functional block diagram of a power controlsub-system capable of being used in the embodiments of the presentinvention;

FIG. 3 shows a series of waveforms utilised in one embodiment of thepresent invention; and

FIG. 4 shows a flowchart of an improved power control algorithm inaccordance with one embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In embodiments of the present invention, a process is adopted wherebythe power amplifier (PA) is brought out of its ‘dead-zone’ before theramp-down signal is applied. In this manner, the power amplifierperformance is modified so that it is capable of reacting rapidly beforethe ramp-down process begins. Thus, the ramp-down process is made moresmooth, for example, at the higher output powers, as the power amplifierhas already come out of its ‘deadzone’. Advantageously, the processimproves the transient behaviour of the wireless subscribercommunication unit when the power amplifier (PA) is ramping down fromhigh output power levels, as well as providing an improved switchingtransient performance.

Referring now to FIG. 1, a block diagram of a subscriber unit, sometimesreferred to as mobile station (MS) or user equipment (UE) 100, isillustrated. The subscriber unit is adapted to support the inventiveconcept of embodiments of the present invention. The subscriber unit 100comprises an antenna 102 coupled to a duplex filter or antenna switch104 that provides isolation between receive and transmit chains withinsubscriber unit 100.

For completeness, the whole architecture of the subscriber unit 100 willbe described, albeit that the inventive concept relates to the poweramplifier and power control operation of the transmitter chain. Thesubscriber unit 100 comprises a receiver chain that includes receiverfront-end circuit 106 (effectively providing reception, filtering andintermediate or base-band frequency conversion). The receiver front-endcircuit 106 receives signal transmissions from another wirelesscommunication unit, for example its associated Base station. Thereceiver front-end circuit 106 is serially coupled to a signalprocessing function (generally realised by a digital signal processor(DSP)) 108. The signal processing function 108 performs de-interleaving,signal demodulation, error correction, data formatting, etc. of thereceived signal. Recovered information from the signal processingfunction 108 is serially coupled to a power control processing function109, which extracts pertinent power control information from thereceived and decoded beacon signal and interprets the information todetermine an appropriate transmit output level for the subscriber unit'stransmissions.

As known in the art, received signals that have been processed by thepower control processing function 109 are typically input to abaseband-processing function 110. The baseband processing device 110takes the received information formatted in a suitable manner and sendsit to an output device 112, such as an audio speaker or liquid crystaldisplay or visual display unit (VDU). A controller 114 controls theinformation flow and operational state of each circuit/element/function.

In different embodiments of the invention, the signal processingfunction 108, power control processing function 109 and basebandprocessing function 110 may be provided within the same physicalsignal-processing device.

A timer 118 is operably coupled to the signal processing functions toprovide synchronisation in both the signal recovery and signalgeneration processes.

As regards the transmit chain, this essentially includes an input device120, such as a microphone or keypad, coupled in series through basebandprocessor 110, a power control processing function 109, signalprocessing function 108, transmitter/modulation circuitry 122 and apower amplifier 124. The signal processing function 108,transmitter/modulation circuitry 122 and the power amplifier 124 areoperationally responsive to the controller 114, with an output from thepower amplifier 124 coupled to the duplex filter or antenna switch 104,as known in the art.

The transmit chain in subscriber unit 100 takes the baseband signal frominput device 120 and converts this into a signal whose level can bebaseband adjusted by the power control processor 109. The power controlprocessor forwards the amplitude-adjusted signal to the signal processor108, where it is encoded for transmission by transmit/modulationcircuitry 122, thereafter amplified by power amplifier 124, and radiatedfrom antenna 102. Clearly, the adjustment of the transmit output powercan be effected by any amplitude or attenuation means in the transmitchain, and the above baseband adjustment is described as one exampleonly.

Notably, in accordance with one embodiment of the present invention, asample of the transmitted signal is fed back to a power control function132. A typical feedback mechanism that can be applied to the abovetransmitter architecture comprises a coupler 128 and a log detector 130.The power control function 132 is also responsive to the power controlprocessor function 109.

The power control processor function 109 monitors the output power ofthe power amplifier by running a saturation detection algorithm in orderto determine whether the power amplifier is saturating. When the poweramplifier is determined as saturating, for example where its performanceis becoming non-linear due to a too-high input power, or due to avarying load, battery supply or temperature, a saturation signal is sethigh by the power amplifier control function 132. When the power controlprocessor function 109 determines that the saturation signal is sethigh, it recognises that a poor transient behaviour may exist during aramp-down operation of the power amplifier 124.

In one embodiment of the present invention, a digital control signal isused to trigger a transmit burst, after which the digital control signalcan initiate a ramp-up operation. Similarly, the digital control signalmay indicate that transmission on the slot has finished as well assubsequently initiate a ramp-down operation. In one embodiment of thepresent invention, in response to determining that the saturation signalis set ‘high’, an improved back-off algorithm is run by the powercontrol processor function 109. In this regard, the power controlprocessor function 109 toggles one or more bit(s) within the digitalsignal prior to the normal toggling of one or more bit(s) or bitsequence that initiate a ramp-down operation.

Furthermore, if the power control processor function 109 initiates theback-off algorithm, then a finite time before ramp-down occurs, a slightnegative perturbation is placed on the target output power. Based on aseries of simulations, the inventors have found that a back-off powerinstigated around 3 μsec. from the start of the ramp-down operationprovides a good performance in a GSM subscriber unit. However, it isenvisaged that in other architectures, or when using other functionalelements or devices, alternative back-off time periods may beappropriate. For example, a suitable time period for GSM ramp-downoperation may be within a specified time range of 1 μsec. to 8 μsec.

In particular, the use of a slight negative perturbation excites theanalog control loop, which in effect brings the power amplifier outputperformance out of its dead-zone a sufficient time before the ramp-downoperation occurs. The ramp-down signal is, thus, applied as normal andcompleted within an appropriate time period after the start of ramp-downoperation. As the analog loop has now already overcome its ‘dead-zone’,the output power tracks the reference ramp smoothly.

In one embodiment of the present invention, the power control processorfunction 109 employs two variable and dynamically adjustable parametersused in the improved power control operation.

A first parameter is a selection of a suitable time (before ramp-down isinitiated) that the power amplifier power is backed off, i.e. a relativetiming when the one or more power control bit(s) is/are toggled.Advantageously, this value can be modified in software.

A second parameter that can be dynamically adjusted is the back-offvalue, to maintain a suitable output power level during the end of thedata transmission burst, whilst meeting the specification requirements.In one embodiment of the present invention, this value isregister-controlled and can be fixed or dynamically adjusted. Theback-off value can be implemented using any known means, such asadjustment of the input signal say via control of an amplification orattenuation function. Alternatively, it is envisaged that adjustment maybe made of the dc power level applied to an amplifier, to reduce theperformance of the amplifier and therefore reduce the gain applied tothe input signal. Notably, in one embodiment, the back-off mechanism isapplied outside of the control loop, thereby avoiding consideration ofsubsequent loop stability issues.

The output power back-off needs to be carefully controlled, as adjustingthe power back-off level by too much may, for example, cause either:

-   -   (i) Power versus time (PvT) to be compromised; or    -   (ii) A large step in the back-off power causes a similar step in        the output power. This could induce poor transients in the power        amplifier, which inadvertently compromises switching transient        performance.

Furthermore, in one embodiment of the present invention, the majority ofthe power control functions may be implemented in a digital signalprocessor (DSP). However, it is within the contemplation of theinvention that the power control processor circuitry described in theabove embodiments can be embodied in any suitable the above embodimentscan be embodied in any suitable form of software, firmware and/orhardware.

Referring now to FIG. 2, a functional block diagram of a the poweramplifier sub-system 200 of a subscriber unit, adapted to incorporatethe present invention, is shown in more detail. The feedback loopcomprises, for example, a log-detector function 130 that allows thefeedback loop to be closed at low (<−5 dBm) power levels. Notably, thecontrol system incorporates an outer loop, comprising log detector 130,analog-to-digital converter 232 and summing junction 204.

A skilled artisan will appreciate that the above circuit configurationis one example of a circuit that can employ the inventive conceptdescribed herein, although it is envisaged that other circuitconfigurations may also benefit from the inventive concepthereindescribed.

The requirements for the analog controller 208 can be stated as follows:

-   -   (i) It must provide a sufficiently high gain to maintain the        bandwidth during ramp-down from high power settings, and    -   (ii) It must provide sufficient gain-phase margin that        ramping-up is not problematic.

A classical two-term PI controller 208 can adequately meet thisrequirement. This has the general form of:

${G(z)} = {{\frac{k_{i}}{s} + k_{p}} = \frac{k_{p}\left( {s + {k_{i}/k_{p}}} \right)}{s}}$

The integral gain term is chosen primarily to ensure adequate loop gainfor the ramp-down condition. The proportional gain term is then selectedto introduce a zero at a specific location, so as to maintain thegain-phase margin.

In one embodiment of the present invention, the value by which the powerlevel is backed off depends on the output power level that is beingtargeted. In this embodiment, it is envisaged that this back-off may belimited to higher output powers only, for example >30 dBm. Adetermination of the output power is made using the signal coupled fromthe coupler 128 at the output of the power amplifier, and detected bylog detector 130.

In one embodiment, the use of a slight negative perturbation applied toinput signal 202 brings the power amplifier output performance out ofits dead-zone. The perturbation is applied a sufficient time before theramp-down operation occurs.

The inventors of the present invention have identified that the poweramplifier responds more slowly at the higher target power levels, andwith an acceptable speed at lower power levels. As such, it is envisagedthat a determination is made as to the target output power, and theimproved back-off algorithm initiated in response to whether the targetoutput power exceeds a threshold power level, such as 30 dBm. Inparticular, simulations and empirical evidence have shown that theoutput power level may be backed off by any value from 0.1 dB to 0.5 dBto provide a reasonable performance that meets the power versus time(PvT) mask.

Referring now to FIG. 3, a series of waveforms utilising the inventiveconcept of the present invention are illustrated. A first waveformindicates the power control level to be applied to the power amplifier202. Notably, in accordance with one embodiment of the presentinvention, the digital code representing the power target is backed-offby a suitable margin 312 (by applying a negative perturbation) at a timeprior to the end of the active transmission of data from the wirelesssubscriber communication unit. In effect, when the detected signal 350is the same as the reference signal 330 then the power output from thepower amplifier 128 (in FIG. 1) represents the desired target power.

A second reference signal 330, for example the signal input to the poweramplifier, is also illustrated. Notably, in accordance with oneembodiment of the present invention, a small perturbation 332 to thepower level is applied to the reference signal due to the back-off powerapplied. This perturbation occurs a suitable time margin prior to theinitiation of the power amplifier ramp-down operation of the wirelesssubscriber communication unit.

Advantageously, the third detected signal waveform 350, shows a smallperturbation to the detected output power level at this suitable timemargin 352 prior to the initiation of the power amplifier ramp-downoperation of the wireless subscriber communication unit. Thisperturbation pulls the power amplifier system outside of its ‘dead-zone’a sufficient time before ramp-down is initiated and thus provides ampletime to remove the loop from its ‘dead-zone’. When ramp-down isinitiated then the power amplifier system is in a healthy bandwidthregion.

This operation is in contrast to the problems encountered with prior artpower amplifiers, particularly those operating at relatively high outputlevels in a closed-loop architecture, where the output power responsecontinues for an extended period of time due to its ‘deadzone’. Thisextended period of time risks encroaching on the outer limit 378 of thePvT mask.

Graph 370 illustrates the output power response 376 of the poweramplifier for output power 380 versus time 385. Thus, as shown in graph370, the output power response 376 of the power amplifier lies withinthe upper threshold 374 and lower threshold 372 power settings, and alsostarts to fall off, in response to the ramp-down operation at thecorrect time.

FIG. 4 shows a flowchart 400 of an improved power control algorithm inaccordance with one embodiment of the present invention. The improvedpower control process is initiated once a transmission burst of data hascommenced, as shown in step 405. A determination is then made as towhether a power amplifier output condition exists, where running theback-off algorithm according to the present invention will enable thetransmitter to operate within the required specification. In thisregard, if the power control processing function of the wirelesssubscriber communication unit has determined that the back-off algorithmshould be run, one or more back-off bit(s) of the control sequence istoggled, in step 410.

A check is then made as to whether the back-off algorithm is enabled, asshown in step 415. If the back-off algorithm is not enabled in step 415,a further determination is then made as to whether the one or moreback-off bit(s) is/are toggled in step 410. If the back-off algorithm isenabled in step 415, the power control level is backed-off by a fixed orvariable amount, as shown in step 420 and as previously described withreference to FIGS. 1-3. A determination is then made as to whether theselected back-off level is optimum, as in step 425.

If the selected back-off level is not optimum, in step 425, the powercontrol level is backed-off by a further fixed or variable amount, asshown in step 420. A further determination is then made as to whetherthe modified back-off level is optimum for this burst, in step 425. Ifthe back-off level is not optimum, it is adjusted on the next burst, asshown in step 428. Thus, in this embodiment, the back-off level may bemodified on a per-burst basis, where the first fixed back-off level is aroughly accurate, and subsequent modification of the power control levelfine tunes the back-off level. In an alternative embodiment, a fixedback-off level is used.

Following a determination as to whether the selected back-off level isoptimum, in step 425, a determination is made as to whether a specifiedtime, prior to the completion of the burst expiring, as shown in step430. If the specified time has not expired, in step 430, the processloops until it has. Once the specified time has expired, in step 430,the power control processing function initiates a ramp-down operation,as shown in step 435.

In one embodiment, a determination is then made as to whether thespecified time is optimum with respect to the PvT mask, as shown in step440. If the specified time is optimum in step 440 the back-off algorithmis completed for this burst. If the specified time is not optimum instep 440, the specified time is adjusted on the next burst, as shown instep 445.

Thus, in this manner, the ramp-down process is improved by performing aback-off of the power control signal a specified time prior tocompletion of the burst. In performing a back-off operation in thismanner, the power-time specification can be met, irrespective of theoutput power level. Furthermore, the back-off level and/or the specifiedtime may be modified to fine-tune the process.

It will be appreciated by a skilled artisan that the inventive conceptsare not limited to a 3G or 2.xG wireless communication device, nor to aclosed-loop transmitter architecture, but are applicable to any wirelesscommunication unit.

It is envisaged that the aforementioned inventive concepts may also beapplied to a large number transceiver architectures and platformsolutions. For example, a semiconductor manufacturer may employ theinventive concepts in a design of a stand-alone RFIC and/or applicationspecific integrated circuit (ASIC) and/or any other sub-system element.

It will be understood that the method and arrangement for closed-looppower control described above provides at least one or more of thefollowing advantages, but may also provide further advantages not solisted:

-   -   (i) A power amplifier operating with a constant envelope        modulation scheme can be run very close to its compression        level, i.e. most efficient operating point, without the known        drawbacks of transient switching effects or power versus time        profiles found in many air-interface protocol specifications,        such as the Global System for Mobile (GSM) communications        standard;    -   (ii) Closed loop PA bandwidth constraints are accounted for        within the power control function;    -   (iii) The power control system is flexible and able to meet the        transient requirements of the system to meet the 3GPP/ETSI 05.05        specification; and    -   (iv) In attempting to optimise the ramp-down process, the power        control back-off level and/or the specified time, before        completion of the burst transmission, may be varied.

The advantages described are merely exemplary. The aforementioned andother advantages may be realized by the embodiments described herein,and not all advantages need be achieved by all embodiments of theinvention.

It will be appreciated that any suitable distribution of functionalitybetween different functional units or signal processing elements, suchas a power control signal processing function, may be used withoutdetracting from the inventive concept herein described.

Hence, references to specific functional devices or elements are only tobe seen as references to suitable means for providing the describedfunctionality, rather than indicative of a strict logical or physicalstructure or organization.

Aspects of the invention may be implemented in any suitable formincluding hardware, software, firmware or any combination of these. Theelements and components of an embodiment of the invention may bephysically, functionally and logically implemented in any suitable way.Indeed, the functionality may be implemented in a single unit or IC, ina plurality of units or ICs or as part of other functional units.

In particular, it is envisaged that the aforementioned inventive conceptcan be applied by a semiconductor manufacturer to any user interface. Itis further envisaged that, for example, a semiconductor manufacturer mayemploy the inventive concept in a design of a stand-alone user interfacefor a computing device or application-specific integrated circuit (ASIC)and/or any other sub-system element.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term ‘comprising’ does not exclude the presence ofother elements or steps.

Furthermore, although individual features may be included in differentclaims, these may possibly be advantageously combined, and the inclusionin different claims does not imply that a combination of features is notfeasible and/or advantageous. Also, the inclusion of a feature in onecategory of claims does not imply a limitation to this category, butrather indicates that the feature is equally applicable to other claimcategories, as appropriate.

Furthermore, the order of features in the claims does not imply anyspecific order in which the features must be performed and in particularthe order of individual steps in a method claim does not imply that thesteps must be performed in this order. Rather, the steps may beperformed in any suitable order. In addition, singular references do notexclude a plurality. Thus, references to “a”, “an”, “first”, “second”etc. do not preclude a plurality.

Thus, a wireless communication having a power control system has beendescribed wherein the aforementioned disadvantages associated with priorart arrangements have been substantially alleviated.

1. A wireless subscriber communication unit comprises a transmittercomprising: a power amplifier; and a closed loop analog feedback powercontrol loop having a power control function arranged to set an outputpower level of the power amplifier, wherein the power control functionperforms a back-off of the output power level, in response to a back-offof a power level provided to the power amplifier, prior to completion ofa transmission burst.
 2. The wireless subscriber communication unitaccording to claim 1 wherein the back-off of the output power level isinitiated by the power control function a specified time beforeinitiating a ramp-down process.
 3. The wireless communication unitaccording to claim 2, wherein the power control function varies thespecified time on a per burst basis.
 4. The wireless subscribercommunication unit according to claim 3 wherein the specified timeranges between 1 μsec and 8 μsec.
 5. The wireless subscribercommunication unit according to claim 2 wherein the power controlfunction performs the back-off of the output power level prior tocompletion of the transmission burst for a subset of a range of outputpower levels.
 6. The wireless communication unit according to claim 2,wherein the power control function performs the back-off of the outputpower level varied on a per burst basis.
 7. The wireless subscribercommunication unit according to claim 2 wherein the back-off of theoutput power level ranges between 0.1 dB and 0.5 dB.
 8. The wirelesssubscriber communication unit according to claim 1 wherein the powercontrol function performs the back-off of the output power level priorto completion of a transmission burst for a subset of a range of outputpower levels.
 9. The wireless communication unit according to claim 1,wherein the power control function performs the back-off of the outputpower level varied on a per burst basis.
 10. The wireless subscribercommunication unit according to claim 9 wherein the back-off of theoutput power level ranges between 0.1 dB and 0.5 dB.
 11. The wirelesscommunication unit according to claim 1, wherein the power controlfunction is operably coupled to a power control processor function andarranged to toggle one or more bit(s) within a digital signal prior toinitiating the back-off of the output power level.
 12. A method of powercontrol in a wireless subscriber communication unit comprising atransmitter having a closed loop analog feedback power control loophaving a power control function, the method comprising the steps of:setting an output power level of the transmitter by the power controlfunction; transmitting a data burst; and performing a back-off of theoutput power level, in response to performing a back-off of a powerlevel provided to a power amplifier, prior to completion of atransmission burst by the power control function.
 13. The methodaccording to claim 12 wherein the step of performing a back-off of theoutput power level comprises performing the back-off a specified timebefore initiating a ramp-down process.
 14. The method according to claim13, wherein the step of performing the back-off of the output powerlevel further comprises varying the specified time on a per burst basis.15. The method according to claim 13 wherein the step of performing theback-off of the output power level comprises performing the back-off ofthe output power level prior to completion of the transmission burst fora subset range of an output power level range.
 16. The method accordingto claim 13, wherein the step of performing the back-off of the outputpower level further comprises varying the back-off level of the outputpower level on a per burst basis.
 17. The method according to claim 12wherein the step of performing the back-off of the output power levelcomprises performing the back-off of the output power level prior tocompletion of the transmission burst for a subset range of an outputpower level range.
 18. The method according to claim 12, wherein thestep of performing the back-off of the output power level furthercomprises varying the back-off level of the output power level on a perburst basis.
 19. The method according to claim 12, wherein the step ofperforming the back-off of the output power level comprises toggling oneor more bit(s) within a digital signal prior to performing the back-offof the output power level.
 20. An integrated circuit for use in awireless communication device comprising: a transmitter; a closed loopanalog feedback power control loop having a power amplifier; and a powercontrol function arranged to set an output power level of thetransmitter, wherein the power control function performs a back-off ofthe output power level, in response to a back-off of a power levelprovided to the power amplifier, prior to completion of a transmissionburst.